Recently, in the ink-jet printing-related industry, which has been significantly growing, realization of high-performance ink-jet printers, improvement of inks, and the like have markedly advanced, and images having high glossiness and high definition, which are substantially equivalent to silver halide prints, have been able to be easily obtained even in ordinary households.
In particular, for inks, improvements for the purpose of realizing high image quality and reducing the environmental burden, for example, a transition from existing dye-based inks to pigment-based inks and a transition from solvent-based inks to water-based inks have been rapidly achieved. Recently, inks containing a water-based pigment ink as a main component have been actively developed.
Furthermore, with the realization of high-performance ink-jet printers and the like, performance at increasingly higher levels has been required for inks year by year. For example, recently, there has been a strong desire for realization of rubfastness at a level at which it is possible to prevent discoloration and degradation of a printed image due to lack of a pigment, the discoloration and degradation being caused by, for example, friction which may be caused when an external force is applied to a surface of the printed image, and durability, such as chemical resistance, at a level at which blurring and discoloration of a printed image are not caused when a cleaning agent such as a glass cleaner adheres to a surface of the printed image without impairing good ejection stability, storage stability, etc. of an ink.
A known example of such an ink having excellent rubfastness is an ink for ink-jet recording, the ink containing a pigment, an aqueous resin, and an aqueous medium, in which the aqueous resin is a polyurethane resin obtained by reacting an organic diisocyanate with a diol having a polyoxyethylene structure, and the polyurethane resin has a carboxyl group, a specific acid value, a specific number-average molecular weight, and a specific amount of the polyoxyethylene structure (refer to, for example, PTL 1).
Images obtained by printing using the above ink for ink-jet recording have a certain degree of rubfastness, and thus, for example, detachment of a pigment due to friction between sheets can be prevented.
However, with the expansion of the field of use of ink-jet printed matter, rubfastness at an even higher level has been desired. Under such circumstances, in a printed image formed using the above-described ink for ink-jet recording, discoloration, degradation, and damaging of the printed image due to detachment of a pigment or the like may be still caused when a strong external force is locally applied to the printed image, for example. In addition, for example, when an alkaline cleaning agent or the like adheres to a surface of an image obtained by printing using the above-described ink for ink-jet recording, there may occur a problem that floating and blurring are generated on the printed surface.
As described above, although an ink-jet printing ink that can form a printed image having both excellent rubfastness and excellent alkali resistance without impairing good ejection stability, storage stability, etc. of the ink has been desired from the industry, an ink-jet printing ink having these properties and a binder for an ink-jet printing ink, the binder being capable of being used in producing the ink, have not yet been found.